Lubricant compositions are used in a variety of industrial applications such as hydraulic oil, air compressor oil, gas compressor oil, gear oil, bearing and circulating system oil, refrigerator compressor oil and steam and gas turbine oils. Conventional lubricant compositions comprise base stocks, co-solvents and additives.
The base stock is in each case selected according to the viscosity that is desired in the envisioned application. Combinations of base stocks of different viscosities, i.e. low and high viscosity respectively, are often used to adjust the needed final viscosity. The co-solvents are used to dissolve polar additives in usually less polar or unpolar base stocks.
The most common additives are antioxidants, detergents, anti-wear additives, metal deactivator, corrosion inhibitors, friction modifiers, extreme-pressure additives, defoamers, anti-foaming agents, viscosity index improvers and demulsifying agents. These additives are used to impart further advantageous properties to the lubricant composition including longer stability and additional protection.
However, after a certain operation time, lubricant compositions have to be replaced due to lubricity loss and/or product degradation. Depending on the machine (engine, gearbox, compressor . . . ) engineering design and the affinity of the lubricant components to adhere to the surface, a certain residue of the lubricant composition (hold-up) remains in the machine, engine, gear etc. it is used in. When being replaced by an unused and possibly different lubricant composition, the used and new lubricants are mixed with each other. Thus, in order to avoid any complications during operation, compatibility between the old and new lubricant is very important.
Depending on their chemical properties a variety of components of lubricant compositions are incompatible with each other, i.e. the mixture of these components leads to oil gelling, phase separation, solidifying or foaming. The oil gelling leads to a dramatic increase of the viscosity which in turn can cause engine problems and can even require the engine to be replaced, if the damage is severe. Hence, when providing novel compounds that are used in lubricant compositions it should always be ensured that these compounds are compatible with compounds that are conventionally used in lubricant compositions.
Besides compatibility with other lubricants, another area of concern is the energy efficiency. The efficiency can be increased if losses are minimized. The losses can be categorized in losses without and with load, their sum being the total losses. Within many parameters which can be influenced by geometry, material etc. lubricant viscosity has a major effect on losses without load, i.e. spilling: Losses with load can be influenced by a low friction coefficient. Thus, at a given viscosity, energy efficiency strongly depends on the friction coefficient of a lubricant.
The friction coefficient can be measured with several methods like Mini-Traction-Machine (MTM), SRV, 2 disc test rig etc. The benefit of a MTM is that one can see the coefficient of friction as an influence of the slide roll ratio. Slide roll ratio describes the difference of the speeds of ball and disc used in the MTM.
U.S. Pat. No. 5,741,947 A describes the copolymerization of cyclic ethers such as polytetrahydrofuran and alkylene oxide in the presence of heteropolyacid catalysts leading to copolymers of random structures. These copolymers are not sufficiently soluble in oils such as mineral oils and polyalphaolefins.